1. Field of the Invention
The present invention relates to an automotive switching member driving circuit, and more particularly to a submergence-responsive switching member driving circuit capable of opening a switching member within a certain period of time (for example, one to five minutes) even when submerged in water.
2. Description of the Prior Art
With reference to FIG. 3, the description will be made of a switching member driving circuit for generally driving an automotive switching member. As shown in FIG. 3, the switching member driving circuit is made up of a CPU31, a driving unit 32, relays RL1 and RL2, transistors TR1 and TR2 and a power terminal VCC.
The CPU31 has a plurality of terminals for input and output, and outputs a very small current that becomes a signal for turning ON/OFF the transistor TR1, TR2 from output terminals (UP, DOWN).
The driving unit 32 is a motor capable of rotating in a forward or reverse direction for switching a switching member (not shown), and in the circuit shown in FIG. 3, when a current flows from an upper side to a lower side, the driving unit 32 rotates (UP) so as to close the switching member, and when the current flows from the lower side to the upper side, the driving unit 32 rotates (DOWN) so as to open the switching member The relays RL1, RL2 have switches SW1, SW2 and exciting coils L1, L2, and only when a control current flows through the exciting coils L1, L2, power supply from the power terminal VCC is structured so as to be supplied to the driving unit 32 through the switches SW1, SW2.
In the transistor TR1, a base is connected to the output terminal UP of the CPU31 through a resistance R3, a collector is connected to the power terminal VCC through the exciting coil L1, and an emitter is grounded.
Also, in the transistor TR2, a base is connected to the output terminal DOWN of the CPU31 through a resistance R4, a collector is connected to the power terminal VCC through the exciting coil L2, and an emitter is grounded.
By the above-described structure, when a close switch or an-open switch (which are not shown) is operated, a signal corresponding to the switch thus operated is inputted into the input terminal of the CPU31, and the CPU31 outputs a signal with a very small current from the output terminal UP or DOWN to the base of the transistors TR1, TR2 in accordance with the signal inputted. The signal outputted causes the transistors TR1, TR2 to turn ON/OFF for causing a control current to flow through the exciting coils L1, L2, whereby the switches SW1, SW2 are changed over to supply on-board power supply (voltage of power terminal VCC) to the driving unit 32. Thereby, the driving unit 32 rotates in a forward/reverse direction to open/close the automotive switching member.
In the case of the circuit shown in FIG. 3, however, potential at point A and point B at both ends of the exciting coil L1 is at the same potential as the power terminal VCC when the driving unit 32 is not driven. If this circuit is submerged in water in this state, there is a short between the point A and point B, and a grounding pattern, the frame grounded or the like existing in the PCB pattern within this circuit.
When there is a short between the point B and the grounding pattern, since a current flows through the exciting coil L1, the switch SW1 is switched on the power terminal VCC side. At this time, since the switch SW2 side is grounded, a current flows through the driving unit 32 to drive the driving unit 32 in a close direction.
Since a similar thing may occur even at point D of the exciting coil L2, the driving unit 32 operates in the forward/reverse direction at random.
In the case where this circuit is used in an on-board power window device, when the window is opened or closed at random under the state that the driver has no intention to operate the window, and under particular conditions that the driver cannot perform calm and adequate judgment or action that the vehicle has been submerged in water, the driver is thrown into a panic, and is cornered into a state in which he cannot judge or act properly within an adequate period of time, which may possibly cause him to be in an increasingly dangerous condition.
Also, when the window operates in a direction to close under the state of affairs that the driver is making an attempt to escape from within the vehicle compartment, it becomes impossible to escape, and there is hidden a danger of being thrown into a panic in the same manner as the foregoing.
In order to avoid this danger, a circuit shown in FIG. 4 has been considered. The circuit shown in FIG. 4 is such that in order to change the method shown in FIG. 3 for performing the control of energization to the exciting coils L1, L2 on the ground side to a method for controlling on the power supply side, each of transistors TR3 and TR4 is interposed between the transistors TR1, TR2 and one end of the exciting coils L1, L2, the emitter is connected to the power terminal VCC and the other end of the exciting coils L1, L2 is grounded.
In the case of the circuit of FIG. 4, potential at point A and point B of the exciting coil L1 or at point C and point D of the exciting coil L2 is at the same potential as the ground potential when the driving unit 32 is not driven. When this circuit is submerged in water in this state, there is a short between the point A and point B, and a grounding pattern existing in the PCB pattern or the like of this circuit, and no current flows through the exciting coil L1 or L2. When, however, there is a short between the emitter of the transistors TR3, TR4 connected to the power terminal VCC for controlling the feed to the coils L1, L2 and the collector connected to the coils, the point B of the exciting coil L1 or the point D of the coil L2 is to short out with the power terminal VCC, and therefore, a current flows through the coil L1 or L2 and there is a possibility that the switching member performs a random switching operation in the same manner as in the circuit shown in FIG. 3.
Also, even though submersion is detected and the driving method for the driving circuit itself to the driving unit is restricted by means of the CPU or the like, if a short is caused in a control portion of a feed switching element (such as relay) to the driving unit within the driving circuit and a malfunction occurs, there is a possibility of performing the same unintended random switching operation as the foregoing.
Further, as this countermeasure, there can also be considered a method for applying a moisture-proof or water-resisting coating to the control portion of the feed switching element (such as relay) to the driving unit within the driving circuit, and the like. However, the coating itself raises the product price, and both regulations on an amount of coating required for those coating to function semi-permanently and management of the amount of coating for actual product assembly are not easy and a possibility of affecting the product price from that aspect is hidden.